Your sketch was probably related to a part that was deleted or changed. To remove the error you just have to edit it and break the link, there will be a little khaki thing that will signal it. You delete it and either you dimension the sketch or fix it so that it is fully constrained, then this error will disappear.
Thank you for the answer, on the other hand I want to keep the function and the sketch for the time being, it is a provisional modification in order to visualize the various impacts.
The question mark does not indicate an error, just that the reference in question is not loaded into memory (to save processing time). This implies that there may be changes that are not taken into account.
If you open the reference (with your assembly in mind), the question mark will disappear.